Photovoltaic cells, sometimes called solar cells, can convert light, such as sunlight, into electrical energy. One type of photovoltaic cell is sometimes called a dye-sensitized solar cell (DSC).
Referring to FIG. 1, one embodiment of a DSC 10 includes a first glass substrate 12 and a second glass substrate 14. Each substrate 12 and 14 has deposited thereon a transparent conducting coating, such as a layer of fluorine-doped tin oxide, 16 and 18, respectively. DSC 10 further includes, sandwiched between substrates 12 and 14, a semiconductor layer 20 (e.g., TiO2 particles), a sensitizing dye layer 22, an electrolyte 24 (e.g., I−/I3−), and a catalyst layer 26 (e.g., Pt). Semiconductor layer 20 is deposited on coating 16 of first substrate 12. Dye layer 22 is sorbed on semiconductor layer 20, e.g., as a monolayer. Together, substrate 12, coating 16, semiconductor layer 20, and dye layer 22 form a working electrode. Catalyst layer 26 is deposited on coating 18 of second substrate 14, and together these components 14, 18, and 26 form a counter electrode. Electrolyte 24 acts as a redox mediator to control the flow of electrons from the counter electrode to the working electrode.
During use, cell 10 undergoes cycles of excitation, oxidation, and reduction that produce a flow of electrons, i.e., electrical energy. Incident light excites dye molecules in dye layer 22. The photoexcited dye molecules then inject electrons into the conduction band of semiconductor layer 20, which leaves the dye molecules oxidized. The injected electrons flow through semiconductor layer 20 to an external load 28 to provide electrical energy. After flowing through load 28, the electrons reduce electrolyte 24 at catalyst layer 26. The reduced electrolyte can then reduce oxidized dye molecules back to their neutral state. This cycle of excitation, oxidation, and reduction is repeated to provide continuous electrical energy to the load.
In some cell fabrication processes, substrate 12, coating 16 and semiconductor layer 20 are sintered at relatively high temperatures, e.g., about 450-500° C., to provide good contact between the semiconductor particles and between the semiconductor layer and the coating. As a result, certain components of a photovoltaic cell can be limited to materials that are stable at relatively high temperatures, such as rigid glass. Limitations on useable materials can, in turn, limit the selection of manufacturing processes, e.g., to batch processes.